Cement bonded materials largely form only mechanical bonds at ambient temperature of 20° Celsius. Adhesion of these ambient temperature cured materials occurs because of the rough surface and while convenient to bond at ambient temperature are comparatively weak as compared to elevated temperature cured material and also tend to suffer from mechanical failure during heat up or when exposed to thermal stresses. Representative of such materials are THERMBOND® refractories that are characterized by chemically bonding both to the cement components and to existing substrates. During the exothermic reaction between dry aggregate and a liquid activator, ionic bonding occurs to form metal-oxide phosphates to provide both coherence and adherence to impart greater strength and durability in chemically aggressive high temperature environments. This material is characterized by a binder system inclusive of alkali phosphates to facilitate ambient temperature set and bonding. Unfortunately, alkali phosphates are characterized by low melting points that limit the high temperature limit of operation for the resulting material. Additionally, the acidity of alkali phosphates precludes introduction of a variety of dispersing or deflocculating agents that otherwise could improve handling properties of the precured cement mixture. As a result, cement strengthening through densification is largely precluded as are often desirable handling methods such as pumping or shotcreting unless extra phosphoric acid is added to improve precured cement mixture flowability and extend working times. However, the addition of more phosphoric acid alters the phosphate:alkali ratio in the precured cement mixture and thereby invariably reduces the strength properties of cement formed with extra phosphoric acid relative to a cast precured cement mixture lacking additional phosphoric acid. As a result of these limitations, alkali phosphate binder system based refractory cements have met with limited acceptance.
Thus, there exists a need for a refractory composition inclusive of a phosphate binder with improved refractory alkali resistance and superior handling properties. There also exists a need for refractory articles formed from such a composition that have an extended operational lifetime relative to conventional refractory articles.